The term “heat transfer” is used to describe thermal energy exchanged between physical systems. Thermal energy exchange can be described as heat dissipation that depends on temperature and pressure. Fundamental modes of heat transfer include conduction or diffusion, convection, and radiation. Heat transfer can also be described as an exchange of kinetic energy between particles through a boundary between two systems at different temperatures from one another, or from their surroundings. Thus, heat transfer occurs from a region of high temperature to another region of lower temperature, changing the internal energy of the systems involved.